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Energy, Work, Power
DEFINITIONS
• ENERGY: the ability to do work.
– When energy is changed to different forms, work
is done.
Unit: Joule (J)
ENERGY
• There are many forms of Energy
• One form can be converted to other forms
• MECHANICAL ENERGY: the energy of an
object because of its position or its motion
– POTENTIAL ENERGY: stored energy
– KINETIC ENERGY: energy of motion
KINETIC ENERGY
• When an object is moved (thrown, pushed,
etc) a force is applied through some distance.
The work done results in motion; the work
becomes kinetic energy.
Ek= ½ mv2
Unit: Joule (J)
POTENTIAL ENERGY
• Potential Energy depends on:
1) The force acting on the object
2) The displacement (change in position) of the
object
Ep=Fd
• For gravitational potential energy:
Ep=mgh
m = mass, g = acceleration due to gravity, h = height
DEFINITIONS
• WORK: the product of force and displacement.
Change in energy.
–
–
–
–
W=Fd
W=ΔE
The force and displacement must be parallel and in
the same direction.
Work is done on an object.
We do work to overcome an opposing force; we do
work to accelerate an object.
A scalar quantity.
Unit: N·m = Joule (J)
DEFINITIONS
• POWER: the rate of doing work; the rate of
using energy.
P=W/t
Unit: J/s which is called a Watt (W)